The invention relates to a media stream transfer technology in the communication field, especially to a communication method and device for preventing media stream circuitry.
In a packet network, particularly in an IP network, the media stream can directly reach the opposite network by the self-addressing characteristic of the IP network to realize the end-to-end communication. Different from signaling, the media stream is not required to be transferred through many session control function entities. However, in the traditional network, in view of the IP address shortage or security, different networks adopt different address domains, even different address formats, such as IPv4 or Ipv6, which results in that two terminals in communication can not address the counterpart directly, so that a network address port translation (NAPT) gateway is needed for translation.
When a calling party is communicating with a called party through a plurality of networks, since the calling party does not know which network the called party is located in at the time of sending the calling request, a plurality of NAPT gateways may be needed for translation during the session establishment procedure so as to realize the media stream connection between the calling party and the called party (when the address domains are different, a NAPT gateway is needed between each two networks for translation).
As shown in FIG. 1, P-AF (Proxy Application Function) represents an application function entity between the access network and the core network, such as the P-CSCF (Proxy Call Session Control Function) in the IMS (Internet Multimedia Subsystem) network.
I-AF (Inter-working Application Function) represents an application function entity for controlling the media layer translation between different core network domain boarders, such as the I-BCF (Inter-working Border Control Function) in the network architecture defined in the TISPAN or ITU-T.
Generally, the P-AF and I-AF represent the signaling layer boarder control function entities.
A/I-BGF (Access Border Gateway Function/Inter-working Border Gateway Function) represents media layer boarder gateway function entities, wherein A represents the place between the access and core networks, I represents the place between different core network domains, the BGF represents the boarder gateway with the NAPT (Network Address Port Translation) function.
As shown in FIG. 1, when the user terminal UE A communicates with the UE B, the communication passes a plurality of networks. Since the address domains of different networks are different, a plurality of BGFs are used for the NAPT translation so as to realize the media stream connection.
In practice, if the bearer network where the user terminal UE A is located can be inter-connected with the bearer network where the user terminal UE B is located, (even if the bearer networks where the user terminals UE A and UE B are located cannot be inter-connected with other middle network domains, these two networks can be inter-connected with each other), the media stream between the UE A and UE B does not need to pass so many BGFs for the NAPT translation.
In addition, in a future packet network, users can be nomadic among different place. If one user subscribes to an operator at site A, the user may access the service network through the IP network or the wireless access network at site B and continue to use services provided by the subscribing place, i.e. the site A. In 3GPP IMS network and in the network architecture defined by the ITU-T and TISPAN, the home subscriber server implements the user's session control. Since the calling party does not know the location of the called party and its bearer network situation when initiating the session (that is, whether the bearer networks of the calling party and the called party are in the same address domain or whether direct addressing can be used), and once some middle bearer networks cannot be inter-connected directly, the NAPT gateway is needed for translation, the traditional session establishment model is bounded the media connection with signaling establishment procedure. For example, when the signaling is passing through some P-AF/I-AF, the media stream will pass through the A/I-BGF. Thus, when the address domains of the bearer networks of locations A and B are different, and a user of location A, who is now at location B, calls a user of location B, the media stream has to return to location A from location B and then to return to location B again for communicating with the called party of location B according to the above model, which results in that the communication between two users, who are actually at location B, has to be in a sequence of from location B to location A-to location B, and has to pass many BGFs for the NAPT translation.
There are many other scenarios of media stream circuitry. The media stream circuitry influences the quality of media stream, results in long transmission time of packets in the network and large delay. If the media stream passes many networks, the uncertainty of the transmission quality increases the uncertainty of the media stream service quality.